Conventionally, as a method of manufacturing a toilet seat formed by joining a seat front member and a seat rear member together, there is a known method of manufacturing a toilet seat in which after a seat front member and a seat rear member are welded to form a joint part, and the joint part is cut and polished using paper, etc., thereby forming a processed surface (for example, see Patent Document 1).                Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2010-99275        